This invention relates to devices for recording, testing, and playing information carrying discs, particularly to the disc positioning, holding, or clamping features and methods associated with such devices; frictional turntables; vibration damping members; and self balancing mechanisms. More particularly, the invention relates to a method and apparatus for automatically clamping compact optical discs.
Optical discs, commonly known as compact discs (CD or CD-ROM) or Digital-Video Discs (DVD or Divx), are an inexpensive and reliable data storage medium. The discs are generally used in conjunction with a playback device (CD player) that rotates the discs on a turntable. In order to allow the CD player to function satisfactorily, it is important to properly locate and securely clamp the disc to the turntable.
Some CD players use spring loaded balls or fingers to clamp the disc against the turntable. The balls or fingers are generally located in a center hub and move in a radial direction relative to the disc's axis of rotation. A spring forces the balls or fingers radially outward with sufficient force to hold the disc against the turntable.
A user wishing to load this type of CD player first places the disc over the hub so that the disc rests on the balls or fingers. The user than applies a downward force to the disc. This downward force biases the balls or fingers in a radially inward direction, which decreases the distance between opposing balls and allows the disc to drop onto the turntable. The spring then returns the balls or fingers to their original position, where they press against the top edge of the disc's center-hole. A user wishing to unload this type of player must pull the disc off the turntable with sufficient force to bias the balls or fingers back into the hub. Once the disk is removed, the spring returns the balls or fingers to their original position.
One of the problems associated with this type of clamping mechanism is the force required to load and unload a disc. The loading and unloading forces cause the disc to flex, which may result in permanent damage. This problem is particularly common when using laminated DVD discs. In addition, users may apply the loading and unloading force in the wrong direction or in a non-uniform fashion. This can cause disc misalignment and damage the CD player. Therefore, there is a need for an improved clamping method that does not require a significant force to load or unload the disc.
Another problem, related to the force required to load and unload the disc, is that users often need to touch the underside of the disk to exert the necessary force. This touch leaves fingerprints on the data storage surface, which can cause the player to incorrectly read the stored information. Yet another problem with this type of clamping mechanism is its complexity for the user. Preferably, a user should be able to drop or insert a disc into the CD player and activate the unit. Therefore, there is also a need for a simple clamp that users can operate conveniently and quickly.
One partial solution to the above-noted problems is called tray loading. CD players using this method generally clamp the disc between a magnet and a steel clamp plate. A cam within the drive mechanism pushes the magnet and the disc into contact with the steel clamp plate. This design, however, is complex and requires significant precision. This design may also cause stray magnetic fields that can disturb the operation of other devices in and around the player. Finally, this design does not tolerate large variations in disc dimensions, and does not always accurately control the force applied to the disc.
Another partial solution is described in U.S. Pat. No. 4,215,535 (Denton). The Denton patent describes a mechanism that uses centripetal force to actuate a clamping device. In particular, clamping members are attached to a turntable and mounted so that they swing radially outward as the turntable accelerates. However, the mechanism cannot provide clamping force at slow speeds, requires a complex interaction between parts, and demands significant manufacturing precision.
U.S. Pat. No. 4,535,255 (Van Alem et al.) describes a compliant clamping mechanism actuated by a continuous spiral spring. The spring forces rollers down a conical surface, which pushes a pressure member against a disc. This mechanism, however, may lose clamping force at high RPM because a centripetal force on the rollers can counteract the spring's force. The clamping force in the Van Alem et al. mechanism may also vary due to thermal expansion and creep in the spring.
U.S. Pat. No. 4,408,839 (Guzik et al.), U.S. Pat. No. 5,014,143 (Mori et al.), and U.S. Pat. No. 5,610,300 (Yamashita et al.) disclose the use of a conical surface to push pressure members against a disc. The conical surface in all three patents is raised and lowered by a rod connected to an external actuator. This actuator, however, requires additional parts and increases manufacturing cost. The actuator must also interact with the turntable shaft, which requires relatively precise tolerances for correct operation.
U.S. Pat. No. 5,555,233 (Yano et al.) discloses a disk clamping device having an operation button. A user wishing to load a disk first rests the disc on a plurality of balls that project from a hub. The user then presses the operation button. This releases a radially outward directed force on the balls, which allows the balls to move radially inward and permits the disc to drop to the turntable. The user then releases the operation button. This restores the radial outward force pushing the balls against the disc. A user wishing to unload the disc must simultaneously depress the operation button to release the balls and lift the disc. Thus, Yano et al. require the user perform several steps to load a disc, which increases complexity and cycle time. Yano et al. also require the user to perform two simultaneous actions to unload the disc. Many users may find this maneuver awkward and time consuming.
Clearly, there is a need for a simple, inexpensive disc clamping mechanism that automatically clamps, holds, and releases a disc as a result of normal disc loading and unloading operations.